A clock formation circuit is used for a digital audio tape recorder (DAT) or a compact disk (CD). Such a clock formation circuit provides a clock signal corresponding to a reference clock signal from a digital data signal formed in synchronization with the reference clock signal.
In the prior art, the clock formation circuit compares a phase of the clock signal to be formed with an inversion timing of the digital data signal and then controls the oscillation frequency of the clock signal so that they are coincidental with each other.
However, the phase comparison is possible only when the frequency difference between the data clock controlling the inversion timing of the digital data signal and the clock signal to be formed falls within the predetermined pulling-in range.
Thus, if the frequency difference falls outside the range, phase comparison between them is impossible. This causes the correct formation clock signal to fail to be formed and prevents the DAT or CD from being positively operated.